Tensioner for a timing chain

Abstract

A tensioner has a base plate and a pivot arm. A first end of the pivot arm is pivotally mounted to the base plate for rotation about a first axis. A spring biases the pivot arm to rotate in a tensioning direction. A push rod assembly is pivotally mounted to the second end of the pivot arm. The push rod assembly is rotatable about a second axis extending parallel to the first axis. The push rod assembly frictionally engages the pivot arm generating frictional forces counter acting and damping the spring bias. When the tensioning guide is forced to rotate in the tensioning direction, the acting moment arm of the push rod force causing the guide to rotate towards the endless drive, is considerable longer at the end of the tensioning stroke than in the beginning of the stroke.

1. A tensioner that is adapted to be coupled to an engine for tensioning an endless power transmitting element, the tensioner comprising:
 a front plate having a bent tab that is configured to locate the tensioner relative to the engine; 
 a base defining a bore and a pair of tool slots, the bore being formed along a first axis and having a first abutment surface, the first abutment surface being centered about the first axis and extending in a circumferential direction, the base being coupled to the front plate such that the front plate closes the bore, the tool slots being formed through the base on a side opposite the front plate and intersecting the bore; 
 a pivot arm disposed within the bore for rotation relative to the base, the pivot arm having a second abutment surface and a first tooling feature, the second abutment surface abutting the first abutment surface and extending in a circumferential direction; 
 a spring biasing the pivot arm about the base in a tensioning direction; and 
 a push rod mounted to the pivot arm for pivotal movement about a second axis that is offset from the first axis, the push rod having a second tooling feature; 
 wherein the first and second tooling features can be aligned to the tool slots through rotation of the pivot arm relative to the base to permit a tool to be inserted through the tool slots and engaged to the first and second tooling features. 
 
     
     
       2. The tensioner of  claim 1 , wherein the first and second tooling features are holes. 
     
     
       3. The tensioner of  claim 1 , further comprising a tensioning guide that is pivotally coupled to the push rod, whereby as the tensioning guide rotates in the tensioning direction, the moment arm of the forces transmitted by the push rod assembly to rotate the tensioning guide will increase. 
     
     
       4. The tensioner of  claim 3 , wherein the moment arm is at least 50 percent larger at the end of travel of the tensioning guide compared to the length of the moment arm at the beginning of travel of the tensioning guide. 
     
     
       5. The tensioner of  claim 1 , wherein the push rod has a fixed length. 
     
     
       6. The tensioner of  claim 1 , wherein contact between the first and second abutment surfaces generates friction forces that tends to inhibit movement of the pivot arm relative to the base. 
     
     
       7. The tensioner of  claim 6 , wherein a frictional damping force resulting from the friction forces generated through contact between the first and second abutment surfaces reaches a predetermined maximum when the push rod assembly is inline with the pivot of the pivot arm. 
     
     
       8. The tensioner of  claim 6 , wherein the pivot arm has a relief along an outer periphery, the relief forming a zone in which contact does not occur between the pivot arm and the base.